1. Field of the Invention
This invention relates to an imaging apparatus for endoscopes in which a TV camera is mounted to the eyepiece section of an endoscope to observe an endoscope image through the TV camera.
2. Description of Related Art
Generally, in order to transmit images, for example, inside a human body, derived from an endoscope to a pickup device, an attachment TV camera is removably mounted at the rear of the eyepiece section of the endoscope. FIG. 1 shows various constructions of an imaging apparatus for endoscopes having such a TV camera attachment. As shown in this figure, conventional imaging apparatuses for endoscopes are roughly divided into the following three combinations according to their applications. In the first case, an endoscope (a rigid endoscope) 1 is connected, through a TV photographic adapter 5 having a focusing function and a TV camera head 7 constructed such that it is separate from the TV photographic adapter 5, to a camera control unit (CCU) 8 so that an image photographed by the TV camera head 7 through the endoscope 1 is displayed on a TV monitor 9. In the second case, the endoscope 1 is connected, such that it is through a TV camera head 13 constructed integral with a TV photographic adapter incorporating an auto-iris device 11, to the CCU 8. In the third case, the endoscope 1 is connected, through an intermediate adapter 14 for focusing and a TV camera head 15 incorporating an imaging optical system 6, to the CCU 8. Here, the endoscope 1 can be used with any one of the TV camera heads 7, 13, or 15 according to its application.
The endoscope 1 comprises an inserting section including an objective lens 2 and a relay lens 3 and an eyepiece section including an eyepiece 4. The objective lens 2 forms an object image Q, which is transmitted to the front of the eyepiece 4 by the relay lens 3 and is re-formed as an image Q'. Light having formed the image Q' emerges from the eyepiece and becomes a nearly parallel light beam. In this way, the object image can be observed through a simple example of eyepiece 4. Also, although the relay lens 3 is drawn in the figure, it is often designed so that image formation is repeated a plural (usually, odd) number of times to transmit the image. The imaging optical system 6, housed in the TV photographic adapter 5 or the TV camera head 13 or 15, receives the light beam leaving the eyepiece 4 of the endoscope 1 and causes the light beam to converge so that the object image Q is formed on a solid-state image sensor 16, such as a CCD, incorporated in the TV camera head 7, 13 or 15.
The TV camera head 13 shown in FIG. 1 is constructed so that when the TV photographic adapter thereof is attached to the eyepiece section of the endoscope 1, the auto-iris device 11 is located at the position where it practically coincides with the exit pupil of the eyepiece 4, and its aperture size can be changed by the driving force of a motor, not shown, provided in the TV photographic adapter. Each of the TV camera heads 7, 13, and 15 is equipped with a filter unit 10 and the CCD 16. An output signal from the CCD 16 is supplied to the CCU 8. The CCU 8 is adapted to convert the output signal into a signal by which the image can be displayed on the TV monitor 9 and to process various signals required. Moreover, the CCU 8 is such that signals for controlling the TV camera and the like are processed when necessary. Reference numeral 12 represents an electric drive path along which a signal for controlling the auto-iris device 11 is transmitted.
When the TV camera head 7 is sterilized, EOG (ethylene oxide gas) and wash water are used, and thus the TV photographic adapter 5 and the TV camera head 7 are designed to have a watertight structure in mutually connecting relation. Specifically, if an O-ring is attached to the connection of either one of the TV photographic adapter 5 and the TV camera head 7, both need not be integrally constructed and can be separated from each other. In this way, various TV photographic adapters can be used as endoscope systems, and hence magnification for observation of an endoscope image which is most suitable for a user's need can be provided. Furthermore, if a focusing ring is used in the TV camera head, it is possible for it to have a focusing function.
In recent years, a sterilization method with a low operating cost has made use of a method of killing all microorganisms by leaving the TV camera head placed, for example, in a high-pressure vapor of 135.degree. C. for five minutes, (i.e., the so-called autoclaving method). This autoclaving method requires that the TV camera head has a fully enclosed structure to prevent water vapor from entering inside the TV camera head. Thus, the TV photographic adapter having the imaging optical system must be constructed such that it is integral with the TV camera head having the CCD so that they are hermetically sealed. Consequently, since a moving part such as a focusing mechanism cannot be provided, it has the problem that the imaging apparatus for endoscopes, including the TV photographic adapter 5 and the TV camera head 7 shown in FIG. 1 cannot be used.
In order to solve this problem, an endoscope imaging apparatus proposed, for example, by Japanese Patent Application No. Hei 6-41395 is available. This apparatus employs the construction including the TV camera head 13 in FIG. 1. The TV camera head 13, instead of having a focusing function, has a variable stop device called the auto-iris to increase the depth of field, and thereby is intended to obviate the out-of-focus defect. Moreover, the apparatus has the merit that the user requires very little focus adjustment.
The prior art imaging apparatus for endoscopes mentioned above is constructed so that the image is formed on the image sensor 16, such as the CCD, in the TV camera head 13 by the imaging optical system 6 disposed behind the eyepiece 4 of the endoscope 1 and can be observed by the monitor 9. This apparatus, however, has the problem of becoming very expensive as a product because the TV camera head 13, although it has autoclaving resistance, has the auto-iris device as well.
Thus, in order to settle this problem, there is an imaging apparatus for endoscopes proposed, for example, by Japanese Patent Application No. Hei 6-22741. This apparatus employs the construction including the TV camera head 15 in FIG. 1. With respect to the TV camera head 15 including the imaging optical system 6 and the CCD 16 and having autoclaving resistance, the apparatus is such that the intermediate adapter 14 for focusing, likewise having autoclaving resistance as a unit, is interposed between the endoscope 1 and the TV camera head 15, and a focusing operation is performed by moving the adapter 14 along the optical axis.
The imaging apparatus for endoscopes constructed as mentioned above, although of autoclaving resistance, can be manufactured at low cost because it has no auto-iris function. However, since the imaging optical system 6 is incorporated in the TV camera head 15, there is the problem that when it is necessary to variously change magnification for observation, the TV camera head 15 must be replaced by another TV camera head having a desired magnification, with a resulting lack of system extension.
In another imaging apparatus for endoscopes of prior art shown in FIG. 2, a TV photographic adapter 25 is removably mounted to the eyepiece section of the endoscope 1 and includes a stop (auto-iris) 31, whose aperture size is variable, and the imaging optical system 6. When the TV photographic adapter 25 is attached to the eyepiece section of the endoscope 1, the stop 31 is located at the position where it practically coincides with the exit pupil of the eyepiece 4, and its aperture size is changed by the driving force of a motor provided in the TV photographic adapter 25. The imaging optical system 6 receives a light beam emerging from the eyepiece 4 and causes the light beam to converge so that when a TV camera head 27 is mounted to the TV photographic adapter 25, the object image is formed on the image sensor 16 such as the CCD. The TV camera head 27 is equipped with the filter unit 10 and the CCD 16. An output signal from the image sensor 16 is supplied to the CCU 8. The CCU 8 is such that the output signal is converted into a signal by which the image can be displayed on the TV monitor 9 and various signals required are processed. Moreover, the CCU 8 is adapted to output signals for controlling the TV camera and the like when necessary. Reference numeral 32 represents electric drive paths along which a signal for controlling the stop 31 is transmitted. Contacts 33 are the connections of the signal lines 32 for controlling the stop 31 and are connected when the TV photographic adapter 25 is attached to the TV camera head 27.
As mentioned above, the conventional apparatus is designed so that the TV photographic adapter 25 having the imaging optical system 6 is mounted behind the eyepiece 4 of the endoscope 1, and the image is formed on the image sensor 16, such as the CCD, in the TV camera head 27 and can be observed by the TV monitor 9 for display.
Also, an outside diameter D of the TV camera head 27 is about 2-3 cm, and a length S where the TV photographic adapter 25 is connected with the TV camera head 27 is a few centimeters.
However, when the image of the endoscope mentioned above is observed by the monitor, there is the problem that the depth of field is small. In recent years, the CCD which is the image sensor of the TV camera has tended toward a high pixel density, which makes a high resolution of an object possible. For this reason, however, since the size of one pixel (pixel pitch) diminishes, an allowable diameter of the circle of confusion must be decreased and the depth of field becomes smaller.
Hence, it is necessary for a rigid-endoscope optical system that, because of a small depth of field, when the endoscope is operated to perform a surgical operation, the imaging optical system 6 is moved back and forth along the optical axis so that the focusing operation is frequently carried out. This practice is not favorable. Recently, in order to improve the depth of field, the variable stop 31 is placed adjacent to the position of the pupil transmitted by the relay system of the endoscope so that when a distant object is observed, the stop 31 is opened to make the object bright, while when a nearby object is observed, it is stopped down because brightness is excessive.
In this case, however, the electric drive paths 32 for driving the stop 31 are required, and for the structure shown in FIG. 2, the electric contacts 33 are required to connect the TV adapter 25 with the TV camera head 27. This structure is inconvenient for sterilization. In the case of an endoscope for medicine in particular, a thorough sterilization treatment of the endoscope after use is indispensable for the prevention of an infectious disease.
Although in the past the sterilization treatment has been made using a gas, such as EOG, and wash water as previously described, sterilization gases are virulently poisonous, as is well known, and in order to ensure the safety of sterilization work, the work becomes elaborate. Furthermore, there is the problem that waste treatment of the wash water is expensive.
In recent years, therefore, a heat sterilization (autoclaving) method which does not require such elaborate working methods is chiefly used in the sterilization work of the endoscope apparatus.
However, for example, in the attachment camera which is removably mounted to the eyepiece section of the endoscope to form the endoscope image, its watertight property is sufficient for ordinary use, but it is difficult to completely seal the camera under conditions of high temperature and pressure in autoclaving treatment. Thus, steam is admitted into the camera and tarnish develops in the optical system. Moreover, for electronic parts, degradation and corrosion may be caused.
In the conventional apparatus, on the other hand, when the autoclaving treatment is made, the electric contacts 33 shown in FIG. 2 cannot be provided on the surfaces of the apparatus, and it is also impossible that, as has been done in the past, for a knob to be mounted outside the TV camera head 27 to manually move the imaging optical system 6.
Thus, as a solution of the above description, FIG. 3 shows a typical structure of a conventional imaging apparatus for endoscopes using an attachment TV camera which has heat resistance to the autoclaving treatment. In this figure, reference numeral 34 denotes a TV camera head and 40 and 42 denote transparent glass (for example, sapphire glass) covers having heat resistance. The endoscope image, after passing through the transparent glass cover 42, is formed on the image sensor 16 by the imaging optical system 6. The filter unit 10, including a low-pass filter and an infrared cut filter, is placed in the optical path. An auto-iris device 38 and the imaging optical system 6 are covered with three layers, formed in order from the inside, of a conductive layer (for example, having the film of an metallic sheath on a cylindrical member) 35, an insulating layer 36, and a metallic layer 37. Reference numeral 39 represents an end supporting member, which holds the three layers.
However, this TV camera head, which has a multi-layer structure, has the problem that it cannot be designed so that, as in the prior art, the imaging optical system 6 is moved by a knob from the outside thereof to perform the focusing operation.
FIG. 4A shows another structure of the conventional imaging apparatus for endoscopes. This apparatus, like that shown in FIG. 3, is such that the TV photographic adapter is constructed integral with the TV camera head. Although the frequency of focusing decreases, work for performing the focusing operation is not eliminated. In the imaging apparatus for endoscopes, as shown in FIG. 4A, a stop unit 46 having the auto-iris 38 is usually shaped into a cylindrical form extending along the optical axis in order to intend radial compactness. Further, a lens barrel 47 holding the imaging optical system 6 is incorporated in the stop unit 46 and is provided with a focus adjusting knob 48. By operating the focus adjusting knob 48 from the outside of an outer frame 45a of the TV camera head 45, the imaging optical system 6 can be moved along the optical axis. FIG. 4B depicts the focus adjusting knob 48 viewed from the side of the TV camera head 45.
The endoscope image captured by the endoscope 1 passes through the glass cover 40 having heat resistance provided at the rear of the endoscope 1 and the glass cover 42 likewise having heat resistance provided at the top of the TV camera head 45, and then is formed on the CCD 16 by the imaging optical system 6. The filter unit 10, including a low-pass filter and an infrared cut filter, is placed immediately before the CCD 16 in the optical path. The focusing operation of the imaging optical system 6 in this imaging apparatus for endoscopes is performed by moving the focus adjusting knob 48 attached to the lens barrel 47 in the directions of arrows of the figure to shift the imaging optical system 6 along the optical axis with respect to the CCD 16.
The optical system used in the imaging apparatus for endoscopes is adapted to receive light not coming directly from an object as in a camera, but emerging from the endoscope. There is a pupil in the endoscope and it is required that the position of the pupil is made to practically coincide with that of the stop of the TV camera head. Hence, even where lenses are moved for focusing, the stop cannot be moved very well. In the apparatus shown in FIG. 4A, when the focusing operation is performed, the stop (auto-iris 38) remains fixed and only the imaging optical system 6 is moved. It is thus required that the lenses are provided in a frame separate from the stop unit 46. Hence, the frame member supporting the imaging optical system 6 has the structure with at least three layers, and the imaging optical system 6 becomes shaky, thus causing decentering. Moreover, since such a conventional apparatus requires the lens barrel 47 and the focus adjusting knob 48, the number of parts is increased.
In the imaging apparatus for endoscopes, the stop has the function of determining the place where the chief ray of the imaging optical system passes. If the relative positions of the stop and the imaging optical system are changed, the ray will traverse a place different from a predetermined place and aberration will be varied or aggravated. It is therefore favorable that the positional relation between the stop and the imaging optical system remains unchanged as far as possible. However, since the conventional apparatus shown in FIG. 4A is designed so that the imaging optical system 6 is moved along the optical axis while fixing the auto-iris 38, the height of the ray passing through the imaging optical system 6 is largely changed by the focusing operation, and aberration of the periphery of the image plane is liable to deteriorate.
In view of the compactness of the TV camera head 45 attached to the endoscope 1, it is necessary to reduce the outer diameter of the imaging optical system 6, corresponding to the thickness of the lens barrel 47 in the stop unit 46. Consequently, an effective marginal beam of the imaging optical system 6 comes to exhibit a tendency to vignetting, and a reduction in the amount of marginal light and ghost and flare caused by the ray striking upon the lens barrel 47 are liable to occur. Conversely, in view of the vignetting of the light beam, if the outer diameter of the stop unit 46 is increased, the compactness of the apparatus cannot be achieved. This is contradictory to the property of the imaging apparatus for endoscopes that its radial dimension must be reduced to a minimum.